Could be a nice idea to bump a few of the noteworthy images to prevent everything from getting buried and forgotten, but eight images each month sounds like a lot. Even assuming you did one every day, which seems rare, that’s not a very harsh selection process (30% pass). Maybe top three sketches would be better? Usually there are a couple of stand-out results that end up better than you were hoping for, but I know I couldn’t find eight I’m prepared to show off.
Alternatively, you could just say “post your favorites” and let each participant decide how many to submit.